Rotative wing aircraft



Oct. 29, 1940.

Filed Jan. 13, 1936 INVENTOR. Hana/d 77/4 Q/y BY 4T0REY Patented Oct.29, 1940 UNITED STATES PATENT OFFICE 2,219,288 ROTATIVE WING AIRCRAFTHarold T. Avery, Oakland, Calif. Application January 13, 1936, SerialNo. 58.917

Claims.

This invention relates to improvements in the blade and hingearrangements of rotative wing aircraft with particular reference tocraft on which the wing systems are alternatively selfrotative or powerdriven.

In my Patent Number 1,993,701 there is disclosed a hinge system forrotative wing aircraft in which each blade or wing is hinged to therotor hub by a single hinge set at an acute angle to the axis of thewing and so angled in elevation as to automatically change the incidenceof the wings into and out of the autorotative range of incidence anglesin response to the power applied to.- the rotor and the condition ofvertical movement of the craft. There is also disclosed in that patentan alternative double hinge arrangement for each blade including meansresponsive to the application of power to the rotor for altering theangle of the hinges. In the single hinge arrangement whatever resultantof the forces acting on any blade is efiective in the plane containingthe hinge and the blade axis, will tend to set up.

stresses in the hinge and bending moments in the blade. The same is trueof the other form disclosed in said patent except that the stresses arelimited by the strength of the springs.

While the aforesaid hinge arrangements also cause the incidence anglesof the blades to be automatically varied to better suit varying flightconditions, the incidence is varied by substantially the same amount atall points in the length of the blade. To best suit flight requirements,however, the variation should be much greater near the roots than nearthe tips of the blades, for the reason that rotational velocity is somuch greater near the tips than near the roots, that'changes in thevertical speed of the craft are proportionately much smaller withrespect to the horizontal air speed of elements of the blades near thetips thereof, and therefore a much smaller change in the relative anglesof air flow is produced near the tips than near the roots of the blades.

One of the objects of the present invention is to provide a hinge systemwhich will automatically vary the incidence angles of the blades intoand out of the range of self rotation, as in the case of the hingesystem of the patent above referred to, and will provide for theautomatic changing of hinge angle, as in the alternative form of hingearrangement referred to in the aforesaid patent, but which will be verymuch simpler than any such arrangement as previously disclosed.

Another object of the invention is to eliminate any tendency of netmoments in the plane of rotation of the hinge and blade axis to set upundue stresses in the hinge or bending moments in the blade. 5

Another object of the invention is to provide a blade and hinge systemwhich will act automatically to vary the incidence angles of the bladesby greater amounts near the roots of the blades than near their tips,thereby maintaining 10 the angles of attack of the blades more nearlyconstant throughout their lengths, under widely different flightconditions.

Another object of the invention is to provide rotative wing aircraftwith a hinge system in-' cluding a plurality of means for automaticallychanging the incidence angles of the blades, which means cooperate witheach other differently in vertical than in horizontal flight and make itpossible to obtain a difierent net change 20 of incidence under each ofthe two conditions of fli ht.

The general principles of the invention will be best understood from thefollowing description of a preferred embodiment thereof, reference beinghad to the accompanying drawing, in which:

Figure l is a plan view of a rotative wing system, embodying the presentinvention; and

Figure 2 is a vertical section taken substantially On line 2-4 of Figure1.

In the drawing, I designates the rotor shaft, which may be connected tothe engine of the craft on which it is mounted by means of any wellknown clutch, either free wheeling or manually operated, substantiallyas disclosed in my patent above referred to, in such a manner as todrive the rotor in the direction indicated by arrow l2. At the upper endof shaft I is a head block 3, in which are rigidly supported a plural-4O ity of hinge pins 4, approximately vertical but with their upper endsslanted inwardly toward the axis of shaft l.

Attached to each hinge pin 4 is a connecting block 5, free to pivotabout hinge pin 4 through a limited angle, as for instance 20 each wayfrom its mean position. Upon reaching the desired limit of its angularmovement in either direction a face of block 5 may engage a face of headblock 3 either directly, or through a resilient block (not shown) so asto prevent further angular displacement. Supported in the outer end ofeach block 5 is a second hinge pin 6 inclined at an acute angle to thelongitudinal axis of the blade and such that its leading end (in thedirecresult in a steepening of the vertical angle tion of rotation ofarrow I2) lies further outwardly with respect to the blade which itsupports than does its trailing end, and also so angled vertically thatits leading end stands higher than its trailing end. Attached to eachhinge pin I is a blade I of the usual airfoil shape comprising a bluntleading and relatively sharp trailing edge. Each blade is arranged forfree pivotal movement about the hinge pin 0, except that its downwardrocking may be limited at a positionthat brings blade I approximatelyhorizontal, by any well known means.

The arrangement is such that as power is applied to shaft I, blades 1will tend to lag back to the limit of their range of movement abouthinge pin 4 until the entire rotor receives suiiicient rotational speedso that centrifugal force acting on the outer part of blade I exerts agreater moment tending to advance. it about hinge 4 than is exerted bythe aerodynamic forces tending to make it lag back of its extreme rearposition.

If power is removed from shaft I, and the rotor allowed to rotate,either under momentum or under aerodynamic forces in flight, the bladewill advance to the position in which its center of gravity lies inapproximately the plane containing the axis of shaft I and the center ofhinge 4 for that blade; butif power is applied to shaft I, blade I willlag back until the line of action of centrifugal force on it, which isthe perpendicular from its center of gravity to the axis of shaft I,passes far enough in the rear of hinge pin 4 to produce a moment'aboutsaid pin 4 equal to the moment being transmitted by shaft I to blade I.Therefore with power applied, blade 1 will lag back with respect to headblock 3, while with power oil it will advance with respect thereto.

Due to the inward slant of hinge pin 4 this of hinge 6 when. power isapplied and a flattening of the angle when power is removed. This willbe apparent when it is considered that any point in swinging about hinge4 will describe a circular path in a plane so angled that the point willreach its highest level when on the side of hinge pin 4 directlyopposite shall; I, and its lowest level when on the side directly towardshaft I. will rise slightly as the blade lags, while the rear endthereof will drop, thus steepening the vertical angle of the hinge, andtending to give the blade asteeper incidence angle during the time poweris applied than is the case with power oil.

, In addition to the effect of angular movements ofthe blade about hingepin 4 on the incidence angle of the blade, the flapping of the bladeabout hinge pin 6 produces a change in incidence angle exactly similarto that outlined in my Patent Number 1,993,701 above referred to.Because hinge pin 6 is angled upward toward its leading end, the bladewill have a considerable plus incidence if the blade is extended outhorizontally from the hinge pin. However, if the blade is rocked upwardabout hinge pin I this incidence angle will be decreased because of thefact that any point in the leading edge of the blade is closer to theaxis of binge pin 6 than is the point of the trailing edge which liesthe same distance from the axis of shaft I, and therefore on the rockingupward of the blade the; trailing point will be raised more than theleading point thereby decreasing the incidence angle.

Therefore the forward end of hinge 8 For instance, in Figure 1, point Iin the leading edge of one of the blades, lies in the same circle ofmovement about the axis of rotary shaft l as does point I in thetrailing edge of the same blade (the two points lying in circle II) butbecause of the fact that the leading end of hinge pin 4 is angledoutward, the point 8 will be closer to the axis of hinge 6 than will thepoint I and therefore in any upward rocking of the blade about hinge 6,the point 8 will not be raised as-much as the point 9.

As set forth in more detail in my Patent Number 1,993,701 above referredto, blade I will be down at low flapping angle when the craft isclimbing vertically under power, due principally to the downwardcomponent of the relative wind engaging the blade; whereas when thecraft is dropping in powerless descent, the blades will be at acomparatively high flapping angle due principally to the upwardcomponent of the relative wind and due also to the decrease incentrifugal force incident to any tendency of the blades to slow down'below their power driven speed of rotation. We will therefore have alarge plus incidence angle during vertical climb and a small plus orslightly negative incidence angle during powerless descent which ideallyadapts the blades for the functions they are called upon to performduring these various types of flight. However, in vertical climb theincidence angle near the'root of the blade should be considerablysteeper than near the tip of the blade because of the fact that theblade elements near the root move through very much less lineal distanceduring a given amount of climb than do the elements near the tip, andtherefore the relative wind has a good deal steeper downward angle inengaging the elements near the root than it does the elements near thetip. However, as the incidence'angle of the blade approaches zero it isdesirable to have approximately equal incidence angle over the entireblade, and as incidence angle becomes negative to have the portion ofthe blade near the root more strongly negative in incidence angle thanthat near the tip.

As shown in Figure 1, the amount of change of incidence angle for anygiven change of flapping angle may be made to be very much greater nearthe root of the blade than near the tip by curving the blade backwardtoward the tip. The amount of change of incidence angle occasioned byany given change of flapping angle is dependent upon the angle which theradius from axis I'to the blade element in question makes with the axisof hinge 6. If this angle is sharp the relative amount of change ofincidence angle is great; but as the radius from axis of shaft I to theblade element approaches a right angle to the axis of hinge 6, theamount of change in the incidence angle of that blade element approacheszero. By curving the blades as shown in Figure 1, the radii from theaxis of shaft I to the blade elements lying along the inner portion ofthe blade, make acute angles with hinge axis 6, thereby insuring a verysubstantial change of incidence angle for any given change of flappingof the entire blade about hinge pin 4 plus only a very slight change ofincidence due to the flapping of the blade about hinge 6, whereas theblade elements near the root receive approximately the same amount ofchange of incidence due to the swinging of the blade about hinge 4 andin addition a large increment of change of incidence due to the flappingof the blade about hinge 6. Thus, in vertical climb, there will be alarge plus incidence to the blade elements near the root and a very muchless plus incidence to the blade elements near the tip; whereas allblade elements can be designed to come back to zero incidence angleapproximately simultaneously in auto rotation and powerless descent andany negative incidence angles due to upward flapping of the blade abouthinge 8 will be much greater near the root of the blade than they willbe near the tip.

When a craft equipped with a rotor such as shown in Figure 1 isadvancing horizontally with the rotor spinning, the air speed of anyblade on the advancing side will be very much greater than that on thereceding side for the reason that the air speed on the advancing sidewill be equal to the air speed of the craft plus the rotational rate ofadvance of the blade; whereas the air speed on the receding side will beequal to the rotational advance of the blade minus the air speed of thecraft. Since centrifugal force will be substantially the same on the twosides, this results in the blades standing at a much higher flappingangle on the advancing side than on the receding side.

With the hinge arrangement disclosed in my Patent 1,993,701 this wouldresult in a very flat incidence angle for the advancing blade and a verysteep positive incidence angle for the receding blade. While this wouldapparently give better rotational characteristics to the rotor than theusual uniform incidence angle throughout, the conditions controlling thevariation in incidence angle during forward flight are so different fromthose controlling it during vertical ascent or descent, that there is noinherent reason why the optimum amount of change of incidence angle fora given change of flapping angle should be the same in horizontal flightas in vertical flight.

The present invention makes it possible to design the range of incidenceangles efiective in vertical flight independently of that in horizontalflight and to have the range of incidence angles in vertical flight asmuch greater than that in horizontal flight as may be desired.

The following considerations will aid in understanding how the presentinvention accomplishes this. In vertical flight maximum climb isobtained with maximum power on the rotor and with the blades atapproximately their minimum flapping angle due, as has already beenpointed out, to the upward movement of the craft giving a downwardcomponent to the relative wind engaging the blades and thereby bringingthem into equilibrium at a low flapping angle. Under these conditionsthe lag of the blades due to the power being applied will tend toincrease the incidence angle, whereas a decrease in flapping anglerotating the blade down about hinge 8 will also tend to increase theincidence angle. Therefore, the effect on incidence angle movement ofthe blade about hinge 4 and the effect of its movement about 'hinge 6are both in the same direction and combine to give a cumulative effecton the incidence angle. Similarly, when the application of power ceasesthe action of centrifugal force advances the blades about hinge pin 4thereby decreasing incidence angle, while the dropping of the craftcreates an upward relative wind, raising the blade about hinge axis 8and further decreasing the incidence angle. Typical numerical examplesof the flapping angles of equilibrium under climb and powerless descentconditions are developed and set forth in my Patent 1,993,701 abovereferred to.

In horizontal flight, on the other hand, the advancing blade encountersmaximum lift and maximum drag due to its maximum air speed which,without corresponding increase in centrifugal force, gives maximumtendency for the blade to flap upward, combined with the maximumtendency for the blade to lag; therefore the lagging movement abouthinge 4 will tend to increase the incidence angle whereas the upwardflapping movement about hinge 6 will tend to decrease the incidenceangle of the advancing blade. The effects on incidence angle of thesetwo hinges therefore, are subtracted, tending to cancel each other inhorizontal flight, whereas they are added together in vertical flight.Therefore, any portion of the desirable change of incidence angle forvertical flight which is obtained due to the angularity of hinge pin 4,will serve to doubly decrease the amount of change of incidence angle inhorizontal flight over that obtained in vertical flight, and thedesigner may, by altering the relative angularity of hinge pin 4 andhinge pin 6, establish his desired range of variation of incidence anglein horizontal flight independently of that in vertical flight.

As has been pointed out, with the blade and hinge arrangements disclosedin my Patent 1,993,701 any resultant force acting in the plane of theblade axis and hinge, tending to rotate the blade about the hinge, wouldtend to set up marked bending moments in the blade itself and heavystresses in the hinge. With the single hinge arrangement disclosed, thisis due to the fact that the blade would not be free to move with respectto the rotor center in the plane containing the blade axis and thehinge. With the alternative disclosure of that patent, in which thehinge axis can be displaced against spring pressures by the resultantblade reactions when the rotor is driven by power from the engine, theblade would still not be free to move in response to forces tending torotate it in the plane of the blade axis and hinge until the resultantof such forces became great enough to overcome the force of the springscontrolling the displacement of the hinge, so that even with thisalternative, the bending moments in the blade and the streses in thehinge would increase until they reached the value at which the limitingsprings yield. In the disclosure of the present invention, on the otherhand, no such moments in the blade, or stresses in the hinge, are set upbecause the blade is free to be displaced about both hinge 6 and hingeii within certain ranges of movement which may stresses set up by the Yto the rotor.

by the application of power to the rotor system in their displacement bycentrifugal force force rather than by the spring arandcontrolledrangement shown in the patent referred to. By

comparing these two disclosures it will be obvi-' ous that the presentdisclosureprovides an un-' usually simple means of accomplishing theselec-.

tive displacement of a blade hinge such as hinge 6 by the application ofpower to therotor system, as well as a desirably simple and eflective Ymeans of accomplishing the other objects set forthhereinabove.

-. by the spirit of the appended claims.-

an angle of approximately 5, on each blade being inclined -oi' bladeseach curved The accompanying drawing illustrates atypical embodiment oi!the invention, with the inner hinge on each blade being approximatelyvertical but converging upwardly toward therotor axis at andthe outerhinge upwardly toward its leadingendv at an angle or approximately 13 tothe plane of rotation, and toward its leading end so as to make an angleaveraging approximately '70" with" the I radius drawn from the rotoraxis to the center 0! pressure 01 the blade.

i With the approximately vertical hinge placed inside the flappinghinge, as shown in the drawing, the skew angle between the flappinghinge and the radius from therotor of pressure of the blade sharper asthe lag of the would be entirely within the blade increased; It scopeof. the present invention to place the flapping hinge inside of the japproximately vertical hinge, in which case the increase of blade lagwould tend' to ,bring the radius from the rotor axis to the center ofpres-' sure of the blade more nearly toward right'ane gles to theflapping hinge. thus decreasing'the/ effective skew of the hinge.

It would be entirely possible to have two a peach blade,- if

proximately vertical hingesior desired, one each side of the flappinghinge, and the relative distances of each-iromtheiiapping hinge can beso designed as to bring thehet change of effective skew within anydesired limits,

templates awide degree of [variation vention therefore is tobeconsideredasfresti'icted only insofar as is required 1 byv ,1. A rotorsystem for aircraft'of theclass described; comprising a rotatably bladesupport,.a plurality of auto-rotatable'bla'des a hin'gexhaving-itsflconnected to s'aid support by I II axis at an acute angle to thelongitudinal axis of said blade, the freeends of of. I

2. In a system of the of the blades to the rotatable memben II tion,.said blades being curved inclined outwardly axis to'the center wouldgrow slightly said blades curving "comprising a rotatable away from thedirection oi'auto-rotation' there I class described, the combination'with a rotatable member of a. p i ityfl toward its outer 1 portion f inthe directionaway from that of rotational advance, and a plurality ofhinges includingahinge having its axis disposed at any acute" im'gle to;

the longitudinal axis of the blade donn'eqtihgeach f "1;1. In a rotaryv3. Ina system oi the class described. the com bination of a powerdriven rotatable member and a plurality of blades hinged thereto byhinges disposed'at an acute angle with their circle oi rotarearwardlywith respect'to the direction of rotation. 1

4.v Arotor system for aircraft oi the'class described comprising ,arotatably mounted blade support, a pl rality of autorotatable blades thefree ends or which curve away from the direction oi' autorotation, andmeans for varying the incidence angles of said blades upon flappingmovement thereof comprising a hinge connection. between each oi' saidblades and said support, each of said hinge connections being disposedat a substantial angle to all elements of the longitudinal axis ot-theassociated blade.

5. In a system of the class described, the comrotatable about a subacuteangle to a plane Pe p ndicular to said axis of rotation. I a

6. In a system ofthe class described, the combination with a rotatablemember, of ablade having its longitudinal I I curved inplan, and a hingeconnecting said blade to said member, said'hinge being at an acute angleto I a 'line'passing. through" the hinge and connecting I any point onthe longitudinal axis ots'aid blade withftheaxisfoi' rotation of saidmember..

7.: A rotor, system for aircraft of the class described comprising, arotatably moimted blade support a plurality'oi' autorotatable bladeseach connectedtosaid S pport by av hinge having its {axisjflxedatzanacuteangleto the axis oi said .s l port, meme. ends of said bladescurving away iromthe direction of autorotation there- 8. A rotor systemfor aircraft 'oi' the class decomprising a .-rotatably mounted bladesupport, a plurality of autorotatable blades each I I II.connectedtoisaid support by a plurality of hinges or the flappin bi geI f acute angle'to the It will be. understood thatthe'inventien eon-q- II I inthe an-' gularity of hinge pins 4 and 6 as. taught herein, as wellas other constructionalvariations' which will occur to those skilledin'th'e .jTherin 1' including a hinge having its axis fixed at an I Iaxis'ot said support, the free ends 01' said blades curving away fromthe directionfoi autorotationthereot- -19. Ina of the class described,the combinationoi a rotatable member, a blade, elements of theaxis ofwhich make'acuate angles rear- I I I I I ffwardly'with,radii"connectingthem to the center the pile art and' ftrailing end thereof. 7

"system adapted to be rotated in flight -from a source .of power or.optionally freely rotatable hub member and a blade 'hinged to saidmember by a plurality of hinges comprising one hinge about whichflapping movement of the blade primarily takes place. the axis or. whichhinge is inclined outwardly and forwardly at an acute angle to a lineparallel to the general lengthwise axis of the blade, and a second hingeabout whichdrag movement of the blade may'takeplacathe axis ot'whichhinge extends upwardly and inwardly.

wing aircraft, arotary'wing 10,1111, .a 'rotary wing aircraft, a rotarywingsystem adapted to be rotated in flight from a source of power oroptionally freely rotatable comprising a rotatable hub member and ablade hinged thereto by two hinges including a flapping hinge, theforward direction of the axis of which with respect to the direction ofrotation of the system is angled upwardly forwardly and outwardly, and adrag hinge, the axis of which extends upwardly and inwardly.

12. In a rotary wing aircraft, a rotary wing system adapted to berotated in flight from a source of power or optionally freely rotatablecomprising a rotatable hub member and a blade hinged thereto by aplurality of hinges comprising a flapping hinge, the forward directionof the axis of which with respect to the direction of rotation of thesystem is angled upwardly forwardly and outwardly, and a drag hinge, theupward direction of the axis of which extends upwardly and inwardly.

13. In a rotary wing aircraft, a rotary wing system adapted to berotated from a source of power or optionally freely rotatable comprisinga rotatable hub member and a blade hinged to said member by a pluralityof hinges comprising one hinge about which flapping movement of theblade primarily takes place, the axis of which hinge is inclinedoutwardly and forwardly at an acute angle to a line parallel to thegeneral lengthwise axis of the blade, and a second hinge about whichdrag movement of the blade may take place, the axis of which hingeextends upwardly and inwardly.

14. In a rotary wing aircraft, a rotary wing system adapted to berotated from a source of power or optionally freely rotatable comprisinga rotatable hub member and a blade hinged thereto by a plurality ofhinges comprising a flapping hinge, the forward clirection'of the axisof which with respect to the direction of rotation of the system isangled upwardly forwardly and outwardly, and a drag hinge, the upwarddirection of the axis of which extends upwardly and inwardly.

15. In a rotary wing aircraft, a rotary wing system adapted to berotated from a source of power or optionally freely rotatable,comprising a rotatable hub member, a blade, and means connecting saidblade to the rotatable hub member including a flapping hinge .the axisof which is angled upwardly and outwardly in the direction of itsrotation, and a drag hinge the axis of which is disposed at an acuteangle with reference to a line parallel to the axis of rotation of saidhub member.

HAROLD T. AVERY.

